Microwave variable reactances



sept.9,1947. HRH-m 2,427,100

' MICROWAV VARIABLE REACTANCES Filed Oct. 26, 1945 ji/Z 4 Y/// 2571A 'Fgz fffff 47 Patented Sept. 9, 1947 UNITED STATES PATENT QFFICE MICROWAVE VARIABLE REACTANCES Harry Kihn, Lawrenceville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October Z6, 1943, Serial No. 507,757

(Cl. FX8- 44) and for adjustably coupling separate sections of.

a waveguide system,

Heretofore; various types of apparatus including tuning stubs, tuning screws, adjustable irises and fixed projections from the inside surfaces of the waveguide faces have been employed for introducing reactance into waveguide transmission systems at predetermined points therein for the purpose of tuning or coupling adjacent waveguide sections. The instant invention contemplates the use of rotatable vanes for introducing either capacitive or inductive reactance at predetermined points in a waveguide transmission system.

Among the objects of the invention are to provide an improved method'of and means for tun-` ing a waveguide transmission system. Another object of the invention is to provide an improved method of and means for selectively introducing reactance into a waveguide. A further object of the invention is to provide an improved method of and means for adjustably coupling adjacent sections of a waveguide transmission system. Another object of the invention is to provide an improved means for adjustably coupling adjacent sections of a waveguide transmission system without introducing objectionable tuning eiects therein.

The invention will be described in further detail by reference to the accompanying drawing of which Figure 1A and 1B are cross-sectional views of a waveguide including reactive elements known in the art, Figures 2A and 2B are crosssectional views of a pair of waveguides including comparable rcactiveelements in accordance with the instant invention, Figure 3 is an elevational cross-sectional view of a preferred embodiment of the invention, Figure 4 is a plan cross-sectional view of the device of Figure 3 taken along the section line 4 4, and Figure 5 is a cross-sectional view of a second embodiment of the invention.

2 tance along the longitudinal axis of the guide. It will be seen that the electrical axis b of the guide is unchanged, while the magnetic axis a is short- `cned in the region of the transverse projecting elements 3, 5. The effect of introducing such transverse conductive elements, is `tointroduce inductance effectively in parallel with the surge impedance of the waveguide system.

`In the waveguide illustrated in Figs. 1 and 2, when using a TEM wave the characteristic impedance is given by 185, published 1942 by McGraw-Hill Book Co.,

V lel with the line surge impedance.

Similar reference characters are applied to similar elements throughout the drawing.

Figures 1A and 1B are illustrative of a known systemjor selectively introducing either inductive or capacitive reactances into a waveguide transmission system. Figure 1A comprises a waveguide I having conductive projections 3, 5 extending transversely from the short side walls of the waveguide to shorten effectively the `magnetic axis a of the waveguide for la predetermineddis- New York).

Therefore, if a is decreased by increasing the sizes of the conductive projections 3, 5, or in any other manner, Zn is increased. Likewise, if b is decreased by closing off the top and bottom of the guide, or in any other manner, Z0 is decreased.

In Figure 1B the transverse projections 3, 5 extend from the wide inner faces of the guide. It will be seen that the magnetic axis a of the guide is unchanged, while the electrical axis b is shortened appreciably. The effect of shortening the electric eld does not appreciably change the cut-oit condition of the section of the waveguide including the transverse projections, but has the effect. of introducing capacitance in paral- It has been calculated that the effective reactance, either positive or negative, introduced by transverse projections of the type described is equal to Where Zo is the characteristic impedance of the waveguide, Z1 is the characteristic impedance of the waveguide in the region of the transverse projecting elements, L is the longitudinal length of the guide in the region of the projecting elements and. ,61 is the propagation constant of the microwaves in the region of the projecting elements, being dependent upon the particular dielectric employed. @Microwave Transmission by J. C. Slater, page 187.) It is evident that if Z1 Zo, then X is positive or equivalent to an inductance. If Z1 Zo, then X is negative and equivalent to a capacitance. V

vFigure 2A comprises a waveguide l having a transverse conductive vane 1 rotatable around the guide axis, the guide is substantially cut-offY thereby since the vane 1 will extend Ventirely across the magnetic axis H of the waveguide.

Figure 2B is similar to Figure 2A exceptr that the vane 1 is rotatable upon thecentral magnetic axis I I of the waveguide. The dimensions of the vane are such that, when it Lis rotated to a plane normal to the longitudinal axis of the waveguide,v

the vane substantially ,interrupts al1 wave propagation along the guide. Rotation of the plane of the vane I1 from Zero to 90 with respect to the longitudinal axis of the waveguide varies the effective inductance introduced in parallel with the waveguide characteristic impedance .from substantially zero to some predetermined maximum value.

Referring to Figures'3 and 4, the vane 'I1 is rotated by means of a shaft yI3 disposed on 'the central magnetic axis ofthe rectangular waveguide I. shaft I5 disposed on the central electrical axis of the rectangular waveguide I. The shafts I3 and I5 are separated at distances of 1A; wavelength alongthe longitudinal axis of the waveguide I. vFor the purpose of illustration, the waveguide is terminated by means of a fixed conductive section I9 to define a cavity 2I enclosing a crystal detector 23. The .particular structure of the crystal detector, and the mounting thereof, does not comprise a part of the instant invention. The particular structure illustrated is well known in the art and comprises suitable clamping and contact means for supporting a cartridge type crystal rdetector in a position substantially coinciding with the central electrical axis of the guide at a point `of the order of 1A; wavelength from the terminating conductive element I9 of the waveguide I. An adjustable series resonant coaxial line 22 is illustrated for tuning out reactance introduced by the detector structure. Output from the crystal detector 23 is obtained from one output terminal 25 thereof and from the adjacentwaveguide face 21. Radio frequency energy is bypassed across the output terminals f25, 21 by means of a relatively large capacitor 29.

Rotation of the horizontal shaft I3 and hence the vane I1 will provide variable capacitive reactance for tun-ing the -crystal cavity 2|. Similarly, rotation of the vertical shaft I5 and hence the vane 1 will rprovide variable inductive reactance -for tuning the crystal .cavity `2l.. The shafts I3, I5 may be rotated manually. For example,onesuitablemanual control is the control knob 3| secured to one end-of the vertical shaft l5 which extends through suitable bearings in the face ofthe waveguide I. If desired, the

control shafts I3, I5 may be ganged byany suit- Similarly, the vane 1 issecured Vto av longitudinally adjustable in a slot 4I along the central magnetic axis of the waveguide I at distances of the order of 1A wavelength along the longitudinal waveguide axis. Preferably, the control shafts 31, 39 are ganged together by any suitable gear or linkage means, not shown, but indicated by the dash line 43. After prelim- "in'ary'adjustrnent of the :relative positions of the Vvanes 33, 35, and the shafts 31, 39,'they may be rotated in unison by means of the coupling means 43 to provide a continuous coupling adjustment -f-or microwave energy transmitted between the input section 45 and the output section 41 of the waveguide I.v

Thus the invention described comprises several modications of a system wherein rotatable vanes are disposed within a waveguide transmission system for adjusting selectively the eiective capacit'ive and inductive reactance introduced into the system in parallel with the waveguide characteristie impedance. Means for separately adjusting 4both tuning and coupling have been described for a typical rectangular waveguide system.

I `claim as my invention:

1. Microwave apparatus including a waveguide transmission system, a rst adjustable reactive element comprising a rst conductive vane coextensive in cross-section and disposed transversely within said waveguide and centrally hinged to rotate on one of the principal transverse axes of said waveguide to introduce inductive reactance into said waveguide, and a second adjustable reactive element comprising a second conductive vane coextensive in cross-section and disposed transversely within said waveguide and centrally hinged at a point substantiallyr of the order of any oddmultiple of one-quarter wavelength from the hinge axis of said first element to rotate on another of the transverse axes of said waveguide to introduce capacitive reactance into said waveguide. v Y

2. Apparatus of the type Ydescribed in claim l including means externa1 of said waveguide for adjusting the angular positions-of said elements.

3. Microwave apparatus including a waveguide transmission system, a firstfadjustable 'reactive element comprising a conductive closuremember disposed transversely within said waveguide and hinged to rotate on one of .the principal transverse axes 'of said waveguide -to introduce inductive reactance into said waveguide, and a second adjustable reactive element comprising a second conductive closure-member disposed transversely within ysaid, Iwaveguide and hinged at a point substantially. any odd `multiple Vof Aone-quarter wavelength from the hinge axis of said rst element to rotate on ,another yof the transverse axes of said waveguide to introduce capacitive reactance into said waveguide.

4. Microwave apparatusincluding a waveguide transmission system, a first adjustable reactive element ydisposed transversely 4within said waveguide .and hinged to rotate on one of the princiadjustable reactive element disposed transversely within .said waveguide at `a point substantially any odd multiple of one quarterwavelength from the .hinge axis of said iirst element and hinged .to rotate .on said same one .of said transverse waveguide axes as said rst element, and means lfor adjusting the angular positions of said elements with respect to said waveguideto vary the attenuation provided in r,said guide .by said elements; e

, 5. Microwave apparatus including la waveguide transmission system, a ilrst adjustable reactive element comprising a conductive closure member disposed transversely within said waveguide and hinged to rotate on one of the principal transverse axes of said Iwaveguide, a second adjustable reactive element comprising a second conductive closure member disposed transversely within said waveguide at a point substann tially any odd multiple of one quarter wavelength from the hinge axis of said rst element and hinged to rotate on said same one of said transverse waveguide axes as said first element, and means for adjusting the angular positions of said elements with respect to said waveguide to vary the attenuation provided in said guide by said elements.

6. Microwave apparatus including a waveguide transmission system, conductive means terminating said system, microwave signal responsive means interposed in said system adjacent said terminating means, a rst adjustable reactive element comprising a conductive closure member disposed transversely within said waveguide and hinged to rotate on one of the principal transverse axes of said waveguide to introduce inductive reactance into said waveguide, and a second adjustable reactive element comprising a second conductive closure member disposed transversely with said waveguide and hinged at a point substantially any odd multiple of one-quarter wavelength from the hinge axis of said first element to rotate on another of the transverse axes of said waveguide to introduce capacitive reactance into said waveguide, said reactive means and said terminating means dening a tunable cavity resonator in said system enclosing said signal responsive means.

7. Microwave apparatus including a waveguide transmission system, conductive means terminating said system, microwave signal response means interposed in said system adjacent said terminating means, a rst adjustable reactive element comprising a conductive closure member disposed transversely within said waveguide and hinged to rotate on one of the principal transverse axes of said waveguide, a second adjustable reactive element comprising a second conductive closure member disposed transversely within said waveguide at a point substantially any odd multiple of one-quarter wavelength from the hinge axis of said first element and hinged to rotate on said same one of said transverse waveguide axes as said rst element, and means for adjusting the angular positions of said elements with respect to said waveguide to vary the attenuation provided in said guide by said elements, said reactive means and said terminating means defining a tunable cavity resonator in said system enclosing said sign nal responsive means.

S. Microwave apparatus including a waveguide connecting a microwave source to a load, a pair of adjustable reactive elements each comprising conductive vanos coextensive in crosssection and disposed transversely within said ywaveguide and each being centrally hinged to rotate on one of the principal transverse axes of said waveguide, said vanes being spaced an odd number of quarter wavelengths along said waveguide between said source and said load, whereby said vanes cooperate to provide adjustable microwave attenuation in said waveguide.

HARRY K11-IN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,129,712 Southworth Sept. 13, 1938 2,180,950 Bowen Nov. 21, 1939 2,206,923 Southworth July 9, 1940 

